to connect a iMac 27" Late 2014 as a display for macbook pro 16"

Target Display Mode support is very limited. Both the slave and the host Mac’s must meet all of the requirements.

carefully read > Use your iMac as a display with target display mode - Apple Support

A 16" MBP is too new to run Target Display Mode, please buy yourself an external display. This is the easiest, most reliable and believe it or not likely least expensive option as it does not require very expensive cabling which won't work anyway.